Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Implant loosening is commonly encountered in humans and other animals that undergo orthopedic surgery and results in compromised construct stability, decreased patient comfort, and additional expenses. The holding power of an implant in bone is associated with multiple factors such as the mechanical and structural properties of the implant, mechanical and physical properties of the bone, placement of the implant, load distribution, and bone-implant integration. Cyclic loading, infection, inflammatory reaction around the implant and subsequent bone resorption, micromotion-induced implant loosening, and fatigue failure at the bone-implant or bone-cement interface are other common causes of implant failure.
Various implant surface configurations, coating methods, and biomaterials have been developed to improve integration between bones and implants. An assortment of osteoinductive and osteoconductive materials has been used to fill bone defects and to anchor implants to bone. To achieve this, a material should adhere implant to bone, tolerate and transfer loads on the implant to bone, promote bone healing, and be readily absorbed at a rate that allows adequate time for osseointegration.
The biomechanical properties of the filler material should resemble those of bone and should be resistant to fragmentation and wear debris formation. Furthermore, the formulation should be easy to apply, should not cause thermal damage during the process of curing, and should be tolerated by the host.
Polymethylmethacrylate is an acrylic bone cement, which has been used for plate luting and total arthroplasties for almost 50 years. Because PMMA is nonabsorbable, two interfaces will inevitably exist: one between the implant and cement and another between the cement and bone. Wear particle formation, thermal necrosis from the curing process, and fractures within the cement layer are known complications associated with the use of PMMA and can lead to failure of the implant construct. Calcium-phosphate cement was the first biodegradable bone cement to be made commercially available. It can tolerate high compressive strength, fill in gaps between implant and bone, act as an osteoconductive medium, and increase biomechanical strength of the bone-implant interface. However, calcium phosphate cement lacks adhesive properties and has a long absorption time.
In addition, existing osteostimulative materials must disadvantageously be applied immediately before implantation. Such a requirement increases the procedure time, and increases the risk of uneven application of the osteostimulative material on an implant.